Design of a broadband low-loss coupled-line multisection symmetrical 3-dB directional coupler in suspended stripline technology

Design of a broadband 3-dB coupled-line directional coupler has been presented. The wide bandwidth has been achieved using symmetrical three-section coupled-line circuit. In order to achieve low-losses of the designed coupler a suspended stripline technology has been chosen. To equalize capacitive and inductive coupling coefficients a recently presented method of capacitive compensation has been utilized and for the first time applied simultaneously in tightly and weakly coupled sections. The measured results of the manufactured directional coupler confirm that the presented design method is suitable for multisection couplers operating in wide frequency range equal in the presented example f₁/f₂=4:1.